To facilitate high fidelity user input and consistent user control across a wide range of experiences and applications, many mobile electronic devices utilize multi-dimensional input modalities. For example, tablets and mobile phones typically provide a touch input surface that tracks finger or stylus position and motion across a two-dimensional area. To accommodate typical human finger coordination and size, the touch sensors and corresponding input surface area in these devices are typically configured to accommodate at least 30 millimeters (mm) of finger motion in each dimension. Typically these devices are also securely supported during user input by resting on a surface or being held in the user's hand.
However, with respect to smaller form factor devices such as eyeglasses and other wearable display devices, the reduced surface area of these devices limits available input modalities. For example, the typically constrained surface area of a pair of eyeglasses makes two-dimensional touch input with human fingers challenging to incorporate. Further, because eyeglasses are typically worn somewhat loosely for comfort, some implementations of touch input functionality may cause undesirable movement of the eyeglasses and corresponding display system.